Technological Field
The description relates to the field of voltage amplifiers, and more particularly to voltage amplifiers operating at low voltage supply.
Description of the Related Technology
Integrated circuits, such as a system on a chip (SoC), have in recent years been subject to substantial decreases in scale of size. Due to such decrease in size, the power consumption per unit area of the analog designs has significantly increased. In energy-aware applications, such as wireless sensor nodes, such high power consumption levels can have a significant influence on the working lifetime of the circuit.
It is known that one method to reduce the power consumption of a circuit is to reduce the supply voltage. Consequently there has been identified a need for a high gain amplifier that can operate at a low voltage to alleviate this issue.
Typical amplifiers obtain a voltage gain by first converting the input voltage to a current, and back to the voltage via an impedance. High gain is obtained by arranging the transistors of such amplifier in a cascade structure to implement a large impedance. However, as the threshold voltage and saturation voltage do not scale down with the voltage supply, the voltage headroom becomes severely limited at a low voltage supply. Such limited voltage headroom restricts the DC gain available to such a voltage amplifier. Accordingly, this dramatically reduces the fidelity of the amplified signal, due to linearity, noise and gain accuracy issues.
In a paper by Shouri Chatterjee, Yannis Tsividis and Peter Kinget, “0.5-V Analog Circuit Techniques and Their Application in OTA and Filter Design,” IEEE Journal of Solid-State Ciruits, pp. 2373-2387, Vol. 40, No. 12, December 2005, the use of cascading low-gain amplifiers to obtain a high gain with a low supply voltage is disclosed. Although a cascading technique such as this may offer an increase in DC gain at a low voltage over conventional amplifiers, this leads to a substantial increase in power.